The present invention relates to a method and to apparatus for oxygen cutting pieces of steel, such as slabs, sheets, billets, and blooms.
The technological background is illustrated by document EP-A-0 639 416 which describes a two-line oxygen cutting installation, in which each line has a moving carriage with an oxygen cutting torch of the pendular or swinging type.
Document EP-A-0 235 588 describes a similar installation using a main torch that performs pendular motion above the piece to be cut transversely, and an additional torch for trimming the cutting bead. Document DE-U-84 28 017 describes another installation for oxygen cutting, which installation uses nozzles placed beneath the slab so as to expel projections horizontally, and nozzles for projecting water, also disposed beneath the slab, for cooling an anti-erosion plate. Reference can also be made to document U.S. Pat. No. 2,820,420 which describes an oxygen cutting torch mounted so as to be cantilevered out on a carriage that can be moved horizontally, and to document WO-A-96/20818 which describes an overhead crane supporting a telescopically extensible vertical working arm.
It is known that the operation of oxygen cutting pieces of steel, and more specifically pieces such as slabs, sheets, billets, and blooms in steel works, generally generates residues of unburnt molten metal on the exit surface for the cutter jet, with a fraction thereof not being expelled into ambient air by the cutter jet but becoming stuck to and solidifying on the exit lips of the cut slot, with this taking place over the entire length of the slot, thereby forming respective cutting beads. These unwanted beads adhere strongly to the bodies of such cut pieces, and it is necessary to implement an additional operation for removing the beads which are of greater or lesser size depending on the grade of steel involved, the cutting speed, and the type and adjustment of oxygen cutting torch. In the past, cutting beads were generally removed either by manual trimming using a torch or a chisel, or else mechanically using an appropriate machine.
Proposals have subsequently been made to trim the cutting bead simultaneously with the bead being formed on the face of the piece in question, as described in document WO-A-99/16570. Nevertheless, that technique makes use of a horizontal cutter jet which means that it is unsuitable for cutting slabs or other products of great width. In addition, the flow of molten metal remains incomplete when using horizontal cutter jets, so detaching the particles that constitute the cutting bead requires a trimming jet that is very powerful in order to be capable of expelling the molten particles downwards. Finally, conventional techniques do not make it possible to avoid the presence of a large amount of smoke in the exit zone of the cutter jet, with such smoke emissions being generated by the post-combustion of unburnt molten metal residues that are ejected by the cutter jet and by the trimmer jet.
The above-mentioned drawbacks have been overcome to a large extent by an oxygen cutting method in which a cutter member is moved in such a manner that the cutter jet is directed towards a first face of the piece in order to attack said piece in a substantially vertical direction so as to form a slot, and synchronously therewith a trimmer member and a spray member are moved in such a manner that their respective jets are directed towards a second face of said piece, opposite from its first face, attacking said second face in an oblique direction at the cutter jet exit so as to trim the cutting bead being formed on said second face while simultaneously reducing smoke emission, said trimmer and spray members being carried by a blade-shaped support passing through the cut slot. Document WO-A-01/28727 in the name of the Applicant describes such an oxygen cutting method in detail together with associated apparatus for implementing the method. The use of a blade-shaped support passing directly through the cut slot is very attractive insofar as all of the active components of the apparatus for implementing the method can be located above the piece to be cut, leaving the space under said piece unoccupied. Nevertheless, it has been found that incidents can arise in operation, e.g. due to excessive cutting speed or to defects in the metal being cut such as inclusions or seams, which incidents can lead to showers of particles being generated in which the particles are constituted by a mixture of molten steel and slag and in which these particles strike the blade-shaped support inside the cut slot. When such incidents or defects occur during the cutting process, the showers of particles can generate obstructions and can even jam the blade-shaped support, preventing it from advancing normally and thus preventing the associated trimmer member from advancing. This makes the cutting and trimming operation insufficiently reliable and makes high cutting speeds completely unattainable.
In addition, when the pieces being cut are slabs coming directly from continuous casting in steel works, the temperatures involved are very high (about 1000xc2x0 C.) such that the blade-shaped support supporting the trimmer member is heated very severely, and such heating can prevent the trimming process from being continued normally.
An object of the invention is to provide a method of oxygen cutting a piece of steel, and apparatus for implementing the method, capable of cutting a wide variety of pieces of steel in regular manner without leaving a cutting bead and without emitting smoke, and above all without running the risk of jamming the forward advance of the trimmer member whose support passes through the cut slot. It is also desirable for the technique to be capable of cutting pieces of steel that come directly from continuous casting.
According to the invention, this problem is solved by a method of oxygen cutting a piece of steel, in which a cutter member is moved in such a manner that the cutter jet is directed towards a first face of the piece in order to attack said face in a substantially vertical direction so as to form a slot, and synchronously therewith a trimmer member and a spray member are moved in such a manner that their respective jets are directed towards a second face of the piece, opposite from its first face, attacking said second face in an oblique direction at the cutter jet exit so as to trim the cutting bead being formed on said second face while simultaneously reducing smoke emission, said trimmer and spray members being carried by a blade-shaped support passing through the cut slot, said method being remarkable in that at least one pressurized fluid jet is projected directly into the cut slot and into the portion thereof which lies between the cutting front and the blade-shaped support, said jet forming a barrier protecting said blade-shaped support against particle projections during advance of the support along the cut slot.
The jet of pressurized fluid thus emitted directly into the cut slot provides a genuine protective barrier or curtain by creating a protected zone in the cut slot, and it does this over the entire thickness of the piece of steel being cut, expelling from the slot all unwanted particles created by the cutter jet. By eliminating any risk of the blade-shaped support being obstructed, it is possible to envisage very high advance speeds while cutting, speeds that are at least twice the advance speeds that can be obtained with traditional oxygen cutting techniques.
In a first implementation of the method of the invention, at least one fluid jet is projected obliquely towards the cutting front, and preferably towards the lower portion of said cutting front. It is then preferable for the selected fluid to be an oxygen cutting fluid, and in particular oxygen or a mixture of oxygen and a fuel gas. The fluid jet projected directly into the cut slot then also makes it possible perform additional cutting in the lower portion of the cutting front, and also makes it possible to deliver additional heat, which improves the performance of the vertical cutting jet, thereby further facilitating advance of the blade-shaped support inside said cut slot.
In a variant implementation, which can be combined with the first implementation specified above, at least one fluid jet is projected towards the blade-shaped support for the trimmer member or towards said member itself. In which case it is preferable for the selected fluid to be a cooling fluid, in particular water or compressed air. The fluid jet projected directly into the cut slot then also performs a function of cooling the blade-shaped support, in addition to providing it with protection against projected particles. This is particularly advantageous when cutting a hot slab that comes directly from continuous casting, where temperature conditions commonly reach 1000xc2x0C.
Also advantageously, the protective jet(s) is/are emitted from one or more projection members moved horizontally synchronously with the cutter, trimmer, and spray members, all of the jets remaining in a common vertical plane.
The invention also provides apparatus for implementing the above-specified oxygen cutting method, the apparatus being of the type comprising a carriage movable horizontally on associated rails over the piece that is to be cut, said carriage carrying a blade-shaped support arranged to pass through the cut slot and supporting at its bottom end trimmer and spray members that pass beneath said piece, the apparatus being remarkable in that said carriage also supports at least one projection member above the piece to be cut and disposed upstream from the blade-shaped support relative to the travel direction of the carriage to project a jet of pressurized fluid directly into the cut slot. It will be understood that by mounting the trimmer, spray, and projection members on the same carriage, it is guaranteed that the horizontal travel of said members is completely synchronous.
Preferably, the carriage also carries a support for a cutter member above the piece to be cut, said cutter member being disposed upstream from said at least one projection member to project an oxygen cutter jet engaging the top face of said piece vertically and forming the cut slot. Thus, all of the cutter, trimmer, spray, and projection members advance in completely synchronous manner during the oxygen cutting process.
It is then preferable for the supports for the various cutter, trimmer, spray, and projection members to be arranged in such a manner that all of the jets emitted by said members remain in a common vertical plane. All of these jets then remain accurately positioned relative to the vertical midplane of the cut slot.
Advantageously, the fluid projection member(s) is/are adjustable in height and/or in inclination.
It is then preferable for the projection member(s) to be adjusted in position in such a manner that the emitted jet(s) is/are directed either towards the cutting front, or towards the blade-shaped support for the trimmer member or towards said member itself. In particular, the projection member(s) is/are connected to sources of oxygen cutting fluid for projection towards the cutting front, or to sources of cooling fluid for projection towards the blade-shaped support of the trimmer member or towards said member.
Also preferably, the blade-shaped support for the trimmer and spray members is vertically retractable in an upward direction, said members also being of a thickness such as to enable them to penetrate into the cut slot. It is then possible to retract the trimmer and spray members to bring them into the cut slot, and thus to retract them completely from beneath the bottom face of the piece to be cut, thus making it possible to go past any obstacles on their path that might be situated beneath the piece of steel that is to be cut and that can arise during advance of the cutter carriage. Such vertical retraction is naturally temporary, and the assembly can then be lowered back down into the oxygen cutting position once the obstacle has been passed.
Provision can then also be made for the blade-shaped support of the trimmer and spray members further to include a hinge enabling pivoting about a horizontal axis so as to bring the trimmer and spray jets into a horizontal plane once the corresponding trimmer and spray members have been fully withdrawn from the cut slot. In this case, when merely retracting these members into the inside of the cut slot does not suffice, said members can be raised above the piece to be cut, after which they can be tilted through 90xc2x0 so as to be brought into a horizontal plane. This avoids the trimmer jet producing negative effects inside the cut slot of the kind that would otherwise arise during partial retraction in order to go past obstacles of large size.